Tài liệu Managing time in relational databases- P22 doc

Glossary Entries include See also: Allen relationship [ fills À1 ]. “assert” cognates Mechanics: the cognate terms “accept”, “agree”, “assent”, “believe”, “claim”, “know”, “say” and “think”. Semantics: terms which, for purposes of the discussions in this book, may be taken as synonymous with “assert” as that word is defined in this book. Comments: • There are important differences among these terms, in the fields of epistemology and semantics. For example, some terms designate what philosophers call “speech acts”, while others designate what philosophers call “propositional attitudes”. 12/31/9999 Mechanics: the latest date which can be represented by the SQL Server DBMS. Semantics: a value for an end date which means that the end of the time period it delimits is unknown but assumed to be later than Now(). Comments: • For other DBMSs, the value used should similarly be the latest date which can be represented by that DBMS. Components: end date, Now(), time period. 9999 Mechanics: a DBMS-agnostic representation of the latest date which can be represented by a specific DBMS. Semantics: a DBMS-agnostic representation of a value for an end date which means that the end of the time period it delimits is unknown but assumed to be later than Now(). Components: end date, Now(), time period. actionable Description: data which is good enough for its intended purposes. Comments: • As a kind of shorthand, we say that the assertion time period of a row is the period of time during which we assert that it is true. And if we discover that a row is incorrect, and does not make a true statement, we do end its assertion time period. • But some true statements are not actionable. For example, a currently effective row in a 100-column table may have 10 of its columns filled with accurate data, and the other 90 columns empty. So that row makes a true statement “as far as it goes”, but because it is so incomplete, it is probably not a statement that provides enough information to act on. • And some actionable statements are not even true. Financial forecasts, for example, may be actionable. But because they are about the future, what they describe hasn’t happened yet, and so they are statements which are neither true nor false. 1 Components: currently asserted. 1 This, at least, is the standard interpretation of Aristotle’s position on what are called “future contingents”, as expressed in his work De Interpretatione. 408 THE ASSERTED VERSIONING GLOSSARY ad hoc query Description: a query which is not embedded in an application program, and which is not run as part of the IT production schedule. Comments: • These queries are usually written by business researchers and analysts, and are often run only a few times before they are discarded. Thus the cost of writing them is amortized over only a few occasions on which they are used, and so it is important to keep the query-writing costs as low as possible. This is why we recommend that, as far as possible, ad hoc queries should be written against views. See also: production query. Allen relationship taxonomy Description: a taxonomy of Allen relationships, developed by the authors and presented in Chapter 3. Comments: • Our Mechanics definitions of the Allen relationships will express time periods as date pairs, using the closed-open convention. The two time periods will be designated P 1 and P 2 , and the begin and end dates, respectively, eff_beg_dt 1 and eff_end_dt 1 , and eff_beg_dt 2 and eff_end_dt 2 . By convention, P 1 is the earlier of the two time periods when one is earlier than the other, and is the shorter of the two time periods otherwise. • These definitions assume that the begin date value for a time period is less than the end date value for that time period. This assumption excludes non-sensical time periods that end before they begin. It also excludes empty time periods. • Our Semantics definitions of the Allen relationships will be stated in terms of clock ticks contained or not contained in time periods, and so these definitions are independent of the convention chosen for using pairs of dates to delimit time periods. In particular, “begin”, “end”, “earlier”, “later” and other terms refer to relationships in time, not to comparisons of begin and/or end dates to other begin and/or end dates. • Boolean operators (AND, OR, NOT) are capitalized. Allen relationship, [ aligns] Mechanics: P 1 and P 2 [align] if and only if ((eff_beg_dt 1 ¼ eff_beg_dt 2 ) AND (eff_end_dt 1 < eff_end_dt 2 )) OR ((eff_beg_dt 1 > eff_beg_dt 2 ) AND (eff_end_dt 1 ¼ eff_end_dt 2 )) AND NOT((eff_beg_dt 1 ¼ eff_beg_dt 2 ) AND (eff_end_dt 1 ¼ eff_end_dt 2 )). Semantics: P 1 and P 2 [align] if and only if they either start or end on the same clock tick, but not both. Allen relationship, [before] Mechanics: P 1 is [before] P 2 if and only if (eff_end_dt 1 < eff_beg_dt 2 ). Semantics: P 1 is [before] P 2 if and only if the next clock tick after P 1 is earlier than the first clock tick in P 2 . Allen relationship, [before À1 ] Mechanics: P 1 is [before À1 ]P 2 if and only if (eff_beg_dt 1 > eff_end_dt 2 ). Semantics: P 1 is [before À1 ]P 2 if and only if the first clock tick in P 1 is later than the next clock tick after P 2 . Allen relationship, [during] Mechanics: P 1 is [during] P 2 if and only if (eff_beg_dt 1 > eff_beg_dt 2 ) AND (eff_end_dt 1 < eff_end_dt 2 ). THE ASSERTED VERSIONING GLOSSARY 409 Semantics: P 1 is [during] P 2 if and only if the first clock tick in P 1 is later than the first clock tick P 2 , and the last clock tick in P 1 is earlier than the last clock tick in P 2 . Allen relationship, [during À1 ] Mechanics: P 1 is [during À1 ]P 2 if and only if (eff_beg_dt 1 < eff_beg_dt 2 ) AND (eff_end_dt 1 > eff_end_dt 2 ). Semantics: P 1 is [during À1 ]P 2 if and only if the first clock tick in P 1 is earlier than the first clock tick in P 2 , and the last clock tick in P 1 is later than the last clock tick in P 2 . Allen relationship, [equals] Mechanics: P 1 [equals]P 2 if and only if (eff_beg_dt 1 ¼ eff_beg_dt 2 ) AND (eff_end_dt 1 ¼ eff_end_dt 2 ). Semantics: P 1 [equals]P 2 if and only if they both start and end on the same clock tick. Allen relationship, [ excludes] Mechanics: P 1 [excludes] P 2 if and only if (eff_end_dt 1 <¼ eff_beg_dt 2 ). Semantics: P 1 [excludes] P 2 if and only if the next clock tick after P 1 is no later than the first clock tick in P 2 . Allen relationship, [ excludes À1 ] Mechanics: P 1 [excludes À1 ]P 2 if and only if (eff_beg_dt 1 >¼ eff_end_dt 2 ). Semantics: P 1 [excludes À1 ]P 2 if and only if the first clock tick in P 1 is no earlier than the next clock tick after P 2 . Allen relationship, [ fills] Mechanics: P 1 [fills] P 2 if and only if (eff_beg_dt 1 >¼ eff_beg_dt 2 ) AND (eff_end_dt 1 <¼ eff_end_dt 2 ). Semantics: P 1 [fills] P 2 if and only if the first clock tick in P 1 is no earlier than the first clock tick in P 2 , and the last clock tick in P 1 is no later than the last clock tick in P 2 . Allen relationship, [ fills À1 ] Mechanics: P 1 [fills À1 ]P 2 if and only if (eff_beg_dt 1 <¼ eff_beg_dt 2 ) AND (eff_end_dt 1 >¼ eff_end_dt 2 ). Semantics: P 1 [fills À1 ]P 2 if and only if the first clock tick in P 1 is no later than the first clock tick in P 2 , and the last clock tick in P 1 is no earlier than the last clock tick in P 2 . Allen relationship, [finishes] Mechanics: P 1 [finishes] P 2 if and only if (eff_beg_dt 1 > eff_beg_dt 2 ) AND (eff_end_dt 1 ¼ eff_end_dt 2 ). Semantics: P 1 [finishes] P 2 if and only if the first clock tick in P 1 is later than the first clock tick in P 2 , and the two time periods end on the same clock tick. Allen relationship, [finishes À1 ] Mechanics: P 1 [finishes À1 ]P 2 if and only if (eff_beg_dt 1 < eff_beg_dt 2 ) AND (eff_end_dt 1 ¼ eff_end_dt 2 ). Semantics: P 1 [finishes À1 ]P 2 if and only if the first clock tick in P 1 is earlier than the first clock tick in P 2 , and the two time periods end on the same clock tick. 410 THE ASSERTED VERSIONING GLOSSARY Allen relationship, [intersects] Mechanics: P 1 [intersects] P 2 if and only if (eff_beg_dt 1 <¼ eff_beg_dt 2 ) AND (eff_end_dt 1 > eff_beg_dt 2 ). Semantics: P 1 [intersects] P 2 if and only if the first clock tick in P 1 is no later than the first clock tick in P 2 , and the next clock tick after P 1 is later than the first clock tick in P 2 . Allen relationship, [ intersects À1 ] Mechanics: P 1 [intersects À1 ]P 2 if and only if (eff_beg_dt 1 >¼ eff_beg_dt 2 ) AND (eff_beg_dt 1 < eff_end_dt 2 ). Semantics: P 1 [intersects À1 ]P 2 if and only if the first clock tick in P 1 is no earlier than the first clock tick in P 2 , and the first clock tick in P 1 is earlier than the next clock tick after P 2 . Allen relationship, [meets] Mechanics: P 1 [meets] P 2 if and only if (eff_end_dt 1 ¼ eff_beg_dt 2 ). Semantics: P 1 [meets] P 2 if and only if the next clock tick after P 1 is the same as the first clock tick in P 2 . Allen relationship, [meets À1 ] Mechanics: P 1 [meets À1 ]P 2 if and only if (eff_beg_dt 1 ¼ eff_end_dt 2 ). Semantics: P 1 [meets À1 ]P 2 if and only if the first clock tick in P 1 is the same as the next clock tick after P 2 . Allen relationship, [ occupies] Mechanics: P 1 [occupies] P 2 if and only if ((eff_beg_dt 1 >¼ eff_beg_dt 2 ) AND (eff_end_dt 1 <¼ eff_end_dt 2 )) AND NOT((eff_beg_dt 1 ¼ eff_beg_dt 2 ) AND (eff_end_dt 1 ¼ eff_end_dt 2 )). Semantics: P 1 [occupies] P 2 if and only if the first clock tick in P 1 is no earlier than the first clock tick in P 2 , and the last clock tick in P 1 is no later than the last clock tick in P 2 ,andP 1 and P 2 do not both begin and end on the same clock tick. Allen relationship, [ occupies À1 ] Mechanics: P 1 [occupies À1 ]P 2 if and only if ((eff_beg_dt 1 <¼ eff_beg_dt 2 ) AND (eff_end_dt 1 >¼ eff_end_dt 2 )) AND NOT((eff_beg_dt 1 ¼ eff_beg_dt 2 ) AND (eff_end_dt 1 ¼ eff_end_dt 2 )). Semantics: P 1 [occupies À1 ]P 2 if and only if the first clock tick in P 1 is no later than the first clock tick in P 2 , and the last clock tick in P 1 is no earlier than the last clock tick in P 2 , and P 1 and P 2 do not both begin and end on the same clock tick. Allen relationship, [overlaps] Mechanics: P 1 [overlaps] P 2 if and only if (eff_beg_dt 1 < eff_beg_dt 2 ) AND (eff_end_dt 1 > eff_beg_dt 2 ) AND (eff_end_dt 1 < eff_end_dt 2 ). Semantics: P 1 [overlaps] P 2 if and only if the first clock tick in P 1 is earlier than the first clock tick in P 2 , and the next clock tick after P 1 is later than the first clock tick in P 2 , and the last clock tick in P 1 is earlier than the last clock tick in P 2 . Allen relationship, [overlaps À1 ] Mechanics: P 1 [overlaps] P 2 if and only if (eff_beg_dt 1 > eff_beg_dt 2 ) AND (eff_beg_dt1 < eff_end_dt 2 ) AND THE ASSERTED VERSIONING GLOSSARY 411 (eff_end_dt 1 > eff_end_dt 2 ). Semantics: P 1 [overlaps À1 ]P 2 if and only if the first clock tick in P 1 is later than the first clock tick in P 2 , and the first clock tick in P 1 is earlier than the next clock tick after the end of P 2 , and the last clock tick in P 1 is later than the last clocktickinP 2 . Allen relationship, [starts] Mechanics: P 1 [starts] P 2 if and only if (eff_beg_dt 1 ¼ eff_beg_dt 2 ) AND (eff_end_dt 1 < eff_end_dt 2 ). Semantics: P 1 [starts] P 2 if and only if the two time periods start on the same clock tick, and the last clock tick in P 1 is earlier than the last clock tick in P 2 . Allen relationship, [starts À1 ] Mechanics: P 1 [starts À1 ]P 2 if and only if (eff_beg_dt 1 ¼ eff_beg_dt 2 ) AND (eff_end_dt 1 > eff_end_dt 2 ). Semantics: P 1 [starts À1 ]P 2 if and only if the two time periods start on the same clock tick, and the last clock tick in P 1 is later than the last clock tick in P 2 . Allen relationships Mechanics: the set of 13 positional relationships between two time periods, a time period and a point in time, or two points in time, as first defined in James F. Allen’s 1983 article Maintaining Knowledge about Temporal Intervals. Semantics: the set of all possible positional relationships between two time periods, a time period and a point in time, or two points in time, defined along a common timeline. Comments: • The Allen relationships are mutually exclusive and jointly exhaustive. • Good discussions of the Allen relationships can also be found in (Snodgrass, 2000), from Chapter 4, and (Date, Darwen and Lorentzos, 2002), from Chapter 6. Components: time period, point in time. approval transaction Mechanics: a transaction that changes the assertion begin date on the assertions in a deferred assertion group to an earlier date. Semantics: a transaction that moves assertions in an deferred assertion group from far future assertion time to near future assertion time. Comments: • The transaction by which deferred assertions are moved close enough to Now() that the business is willing to let them become current by means of the passage of time. See also: fall into currency. Components: assertion, assertion begin date, deferred assertion group, far future assertion time, near future assertion time. as-is Mechanics: data whose assertion begin date is earlier than Now() and whose assertion end date is later than Now(). Semantics: data whose assertion time period is current. Comments: • See also: as-was. The as-is vs. as-was distinction is often confused with the distinction between current and past versions. Many best practices implementations of versioning do not distinguish between the two, and therefore introduce ambiguities into their temporal semantics. Components: assertion begin date, assertion end date, assertion time period, Now(). 412 THE ASSERTED VERSIONING GLOSSARY assert Mechanics: to place a row in an asserted version table in current assertion time. Semantics: to claim that a row in an asserted version table makes a true and/or actionable statement. Components: actionable, asserted version table, current assertion, statement. asserted version table Mechanics: a bi-temporal table in which each row can exist in past, present or future assertion time, and also in past, present or future effective time. Semantics: a table each of whose rows indicates when the object it represents is as its business data describes it, and when that row is claimed to make a true and/or actionable statement about that object. Comments: • In contrast, rows in bi-temporal tables of the standard temporal model cannot exist in future assertion time. • Also, a table whose structure conforms to the schema presented in Chapter 6. See also: bi-temporal data canonical form. Components: actionable, assertion time, bi-temporal table, business data, effective time, object, statement, the standard temporal model. Asserted Versioning database Mechanics: a database that contains at least one asserted version table. Components: asserted version table. Asserted Versioning Framework Mechanics : software which (i) generates asserted ve rsion tables from logica l data models and associated metadata; (ii) enforces temporal entity integrity and temporal referential integrity constraints as asserted version tables are maintained; (iii) translates temporal insert, update and delete transactions into the physical transactions which maintain an asserted version table; and (iv) internalizes pipeline datasets. Comments: • The Asserted Versioning Framework is software developed by the authors which implements Asserted Versioning. Components: asserted version table, internalization of pipeline datasets, physical transaction, temporal data management, temporal entity integrity, temporal referential integrity, temporal transaction. assertion Mechanics: the temporally delimited claim that a row in an asserted version table makes a true and/or actionable statement about what the object it represents is like during the time period designated by that version of that object. Semantics: the claim that a statement is true and/or actionable. Components: actionable, asserted version table, object, represent, statement, time period, version. assertion approval date Mechanics: the new assertion begin date which an approval transaction specifies for the assertions in a deferred assertion group. Semantics: the near future assertion time date to which all assertions in a deferred assertion group are to be retrograde moved. Components: approval transaction, assertion, assertion begin date, deferred assertion group, near future assertion time, retrograde movement. THE ASSERTED VERSIONING GLOSSARY 413 assertion begin date Mechanics: the begin date of the assertion time period of a row in an asserted version table. Semantics: the date indicating when a version begins to be asserted as a true and/ or actionable statement of what its object is like during its indicated period of effective time. Comments: • A row can never be inserted with an assertion begin date in the past, because an assertion cannot exist prior to the row whose truth it asserts. See also: temporalized extension of the Closed World Assumption. • But a row can be inserted with an assertion begin date in the future because when that future date comes to pass, the row will already exist. See also: deferred assertion. Components: actionable, assert, assertion time period, asserted version table, begin date, effective time period, object, version. assertion end date Mechanics: the date on which the assertion time period of a r ow i n an asserted version table ends, or a date indicating that the end of the assertion time period is u nknown but presumed to be later than Now(). Semantics: the date indicating when a version stops being asserted as a true and/ or actionable statement of what its object is like during its indicated period of effective time, or indicating that the end of the assertion time period is unknown but presumed to be later than Now(). Comments: • An assertion end date is always set to 9999 when its row is inserted. It retains that value unless and until that assertion is withdrawn. Components: actionable, assertion time period, asserted version table, effective time period, end date, Now(), object, statement, version. assertion group Mechanics: a group of one or more deferred assertions, sharing the same assertion begin date. Semantics: a group of one or more assertions sharing the same future assertion time period. Components: assertion, assertion begin date, deferred assertion, future assertion time period. assertion group date Mechanics: the assertion begin date on a group of one or more deferred assertions. Semantics: the date which indicates when a group of deferred assertions will become currently asserted. Comments: • This date is also the unique identifier of an assertion group. Components: assertion begin date, currently asserted, deferred assertion. assertion table Mechanics: a uni-temporal table whose explicitly represented time is assertion time. Semantics: a uni-temporal table each of whose rows is a temporally delimited assertion about what its object is like Now(). Components: uni-temporal, assertion, assertion time, Now(), object. 414 THE ASSERTED VERSIONING GLOSSARY assertion time Mechanics: a series of clock ticks, extending from the earliest to the latest clock ticks which the DBMS can recognize, within which assertion begin and end dates are located. Semantics: the temporal dimension which interprets a time period associated with a row as indicating when that row is asserted to be true. Components: assertion begin date, assertion end date, clock tick, temporal dimension, time period. assertion time period Mechanics: a time period in assertion time associated with a specific row in an asserted version table. Semantics: the period of time during which a row in an asserted version table is claimed to make a true and/or actionable statement. Components: actionable, asserted version table, assertion time, statement, time period. as-was Mechanics: data whose assertion end date is earlier than Now(). Semantics: data whose assertion time period is past. Comments: • See also: as-is. The as-was vs. as-is distinction is an assertion time distinction, but in supporting temporal data management in their databases, IT professionals often confuse this distinction with the effective time distinction between past and current versions. Components: assertion end date, assertion time period, Now(). atomic clock tick Mechanics: the smallest unit of time kept by a computer’s clock that can be recognized by a specific DBMS. Semantics: a unit of time that is indivisible for purposes of temporal data management. Comments: • See also: clock tick. Components: N/A. AVF See Asserted Versioning Framework. basic temporal transaction Mechanics: a temporal transaction which does not specify any temporal parameters. Semantics: a temporal transaction which accepts the default va lues for its temporal parameters, those being an effective be gin date of Now(), an effective end date of 9999, an assertion begin date of Now() and an assertion end date of 9999. Comments: • Assertion end dates are the one temporal parameter that cannot be specified on temporal transactions. All temporal transactions, including basic ones, create asserted version rows with an assertion end date of 9999. Components: assertion begin date, assertion end date, effective begin date, effective end date, Now(), temporal parameter, temporal transaction. THE ASSERTED VERSIONING GLOSSARY 415 basic versioning Mechanics: a form of versioning in which a version date is added to the primary key of an otherwise non-temporal table. Semantics: a form of versioning in which all versions of the same object are contiguous. Comments: • Basic versioning is not part of Asserted Versioning. It is a form of best practices versioning. See Chapter 4. • See also: logical delete versioning, temporal gap versioning, effective time versioning. Components: contiguous, object, non-temporal table, version. begin date Mechanics: an assertion begin date or an effective begin date. Semantics: a date which marks the start of an assertion or an effective time period. Components: assertion begin date, assertion time period, effective begin date, effective time period. bi-temporal data canonical form Mechanics: the schema common to all asserted version tables. Semantics: a single schema which can express the full range of bi-temporal semantics. Comments: • Any history table, logfile, or version table can be transformed into an asserted version table without loss of content. Components: asserted version table, bi-temporal. bi-temporal database Mechanics: a database containing at least one bi-temporal table. Components: bi-temporal table. bi-temporal envelope Semantics: a specified effective time period, included within a specified assertion time period. Comments: • The temporal scope of every temporal transaction is delimited by the bi-temporal envelope specified on the transaction. • Every row in an asserted version table exists in a bi-temporal envelope. Components: assertion time period, effective time period, include. bi-temporal table Mechanics: a table whose rows contain one pair of dates which define an epistemological time period, and a second pair of dates which define an ontological time period. Semantics: a table whose rows contain data about both the past, the present and the future of things, and also about the past and the present of our beliefs about those things. Comments. • See also: epistemological time, ontological time. Components: “assert” cognate (belief), epistemological time, ontological time, thing, time period. 416 THE ASSERTED VERSIONING GLOSSARY business data Mechanics: all columns of an asserted version table other than those columns which implement Asserted Versioning. Semantics: the columns of data which record the properties or relationships of objects during one or more periods of effective time. Components: asserted version table, effective time, object. business key Mechanics: the primary key of the entity in the logical data model from which an asserted version table is generated. Semantics: the u nique identifier f or an o bject as represented i n a non-temporal table. Comments: • If a surrogate key is used in the logical data model, this surrogate key is used as the business key in an asserted version table. Components: asserted version table, non-temporal table, object. child managed object Mechanics: a version in a TRI relationship. Semantics: a managed object which represents a child object in a TRI relationship. Components: child object, TRI, version. child object Semantics: an object, represented by a managed object, which is existence- dependent on another object, also represented by a managed object. Components: existence dependency, managed object, object, represent. child row Mechanics: a row in an asserted version table which contains a non-null temporal foreign key. Semantics: a version which represents an object which is existence-dependent on some other object. Comments: • The various “parent” and “child” expressions also apply to conventional tables, of course, in which case the relationship involved is referential integrity, not temporal referential integrity. But in this Glossary, we are explicitly defining these expressions as they apply to asserted version tables. Components: asserted version table, existence dependency, object, temporal foreign key. child table Mechanics: a table which contains at least one temporal foreign key. Semantics: a table whose rows represent child objects. Components: child object, temporal foreign key. child version Mechanics: a version in an asserted version table X is a child to an episode in asserted version table Y if and only if the version in X has a temporal foreign key whose value is identical to the value of the object identifier of that episode in Y, and the effective time period of that episode in Y [fills À1 ] the effective time period of that version in X. Semantics: a version in an asserted version table X is a child to an episode in asserted version table Y if and only if the object for that version in X is THE ASSERTED VERSIONING GLOSSARY 417 [...]... clock ticks Components: assertion time period, clock tick, effective time period contiguous Mechanics: time period or point in time X is contiguous with time period or point in time Y if and only if either X [meets] Y or X [meetsÀ1] Y Components: Allen relationship [meets], Allen relationship [meetsÀ1], point in time, time period conventional data Mechanics: data in a conventional table Semantics:... version table Semantics: the transition from one point in effective time or assertion time to the next point in effective time or assertion time, according to the chosen granularity which defines those two points in time as contiguous Comments: • Note that chronons are atomic clock ticks, not clock ticks • A 1-month-per-tick clock represents a situation in which a database is updated at most once a month... to internal business users or exported to outside users, or are augmented as they move along an “outflow data pipeline” leading to a final state in which they are delivered to internal business users or outside users • The various kinds of external pipeline datasets do not form a partitioning Most of these names are in fairly widespread usage, but no standard definition of them exists Therefore, in. .. effective time versioning Mechanics: a form of versioning similar to temporal gap versioning, but in which a row create date is added to each version, in addition to a version begin date and a version end date Semantics: a form of versioning in which versions of the same object may or may not be contiguous, in which no version is physically deleted, in which the version dates delimit an effective time period,... statement, time period event Semantics: a point in time or a period of time during which one or more objects come into existence, change from one state to another state, or go out of existence Comments: • Events are the occasions on which changes happen to persistent objects As events, they have two important features: (i) they occur at a point in time, or sometimes last for a limited period of time; and... this is called an inference engine While relational databases are the principal way that software helps us reason about instances, inference engines are the principal way that software helps us reason about types Reasoning about types is what formal ontology is about It is not often recognized that formal ontology and relational databases are complementary in this way, as means of reasoning about, respectively,... and in which the date the row was physically created is also provided Comments: • Effective time versioning is not part of Asserted Versioning See Chapter 4 • See also: basic versioning, logical delete versioning, temporal gap versioning Components: contiguous, effective time period, object, row create date, temporal gap versioning, version, version begin date, version end date empty assertion time. .. Versioning Framework, persistent object, seamless access, temporal data management taxonomy (queryable temporal data) / (state temporal data) / (bi-temporal data), temporal entity integrity, temporal referential integrity episode Mechanics: within shared assertion time, a series or one or more rows representing the same object in which, in effective time, each non-initial row [meets] the next one, in which... time period begins Comments: • The effective begin date of an episode is the effective begin date of its earliest version Components: closed-open, effective time period effective end date Mechanics: using the closed-open convention, the first date after the last date in an effective time period 423 424 THE ASSERTED VERSIONING GLOSSARY Semantics: the date indicating when an effective time period ends... Semantics: a flag which distinguishes between rows which are definitely known to be in the assertion time past from all other rows (See Chapter 15) Components: Asserted Versioning Framework, asserted version table, assertion time clock tick Mechanics: the unit of time used for effective begin and end dates, assertion begin and end dates, episode begin dates and row create dates, in an asserted version table . between two time periods, a time period and a point in time, or two points in time, as first defined in James F. Allen’s 1983 article Maintaining Knowledge. assertion time period, clock tick, effective time period. contiguous Mechanics: time period or point in time X is contiguous with time period or point in time